The present invention relates to pressure-sensitive adhesive constructions and methods for making the same and, more particularly, to prelaminate pressure-sensitive adhesive constructions having a detackified surface to provide anti-blocking characteristics for facilitating subsequent handling and/or treatment of the construction before lamination to a second substrate.
Pressure-sensitive adhesive (PSA) constructions such as labels, tapes, decals and the like are known in the art. For example, PSA label constructions are commonly used to apply a particular face stock having a specific nature of printing to an object or article, and are especially useful where objects having low surface energies are to be labeled. PSA label constructions typically comprise a face stock, a liner, and a PSA layer interposed between the face stock and liner.
In accordance with well known practice in the industry, the liner may be coated with a releasable material, forming a release liner. The releasable surface of the release liner may be coated with a layer of PSA for subsequent transfer of the adhesive to the face stock with which the release liner is employed. When the face stock is combined with the release liner, the adhesive is laminated to the face stock. Alternatively, the adhesive may have been directly coated on or combined with the face stock prior to combining the face stock with the release liner. In either approach, in a later step the release liner is removed from the PSA and face stock construction to expose the adhesive, which remains permanently joined to the face stock.
Thus, as indicated in FIG. 1, a PSA 10 may be applied to the release surface of the release liner 12 at a station 14 following drying or curing of a release coat 16 previously applied to the release liner at station 18. This may be a tandem coating operation, or the adhesive coating 10 may be applied on a separate coating line. The PSA may be formed from a material that requires drying before application of the face stock, in which case the face stock is applied to the dried PSA layer. In some cases the release surface 16 is precoated onto the release liner 12, and the adhesive 10 is applied at a later time prior to laminating the release liner 12 to a face stock 20. The combining of the release liner and face stock is diagrammatically illustrated in FIG. 2.
Most commonly, the resulting laminated construction takes the form of a continuous ribbon or web that is collected on a roll. This roll may be transported to a converter for further operations such as printing, die cutting, and matrix stripping, in order to create labels, signs, or other PSA products. Thus for example, FIG. 3 illustrates the die cutting of the face stock 20 at a station 22 into a series of PSA labels 24 of desired shape and size, carried by the release liner 12.
The manufacturing processes described above share the characteristic that the lamination of the release liner, PSA, and face stock occur at a common production facility. To promote flexibility in the production of PSA constructions, it is desired to devise a method for coating the release liner with a PSA (thereby forming a xe2x80x9cprelaminate constructionxe2x80x9d) in a separate and independent operation from laminating the prelaminate construction to face stock. These operations should be capable, for example, of allowing the prelaminate construction to be produced at a different geographic location, or in a separate and independent production line, than that at which the prelaminate construction is laminated to the face stock.
One way in which this desire has been addressed has been to make PSA constructions having a subsequent layer of material applied to the exposed surface of the adhesive in an effort to detackify the adhesive surface. Detackifying the PSA construction in such manner has been thought to be an effective way of forming a nonblocking PSA construction that, in theory, would permit the prelaminate PSA construction to be rolled upon itself and stored or transported for subsequent lamination without adhering to a backside surface of the construction, or to anything else. In practice, however, detackified PSA constructions known in the art have not been entirely effective at providing a completely nonblocking construction.
As used herein, the term xe2x80x9cnonblockingxe2x80x9d is intended to mean that the prelaminate PSA construction is capable of preventing any significant bonding or adhering to contiguous layers of the label construction, i.e., the backside surface of the release liner, during storage, transportation and handling of the construction so that the removal or separation of the prelaminate PSA construction from contiguous layers of the construction, when collected and/or stored in sheet or roll form, will not be impaired.
For example, U.S. Pat. No. 4,135,033 discloses a two-layer adhesive coating having a dry, nontacky surface that is convertible to a permanently adhesive surface by application of heat over a period of ten seconds. The two-layer adhesive coating can be used with silicone treated release paper. In manufacturing PSA constructions it is desired that the step of heating and laminating the PSA construction be completed quickly to maximize the web speed and, thereby maximize manufacturing efficiency. The need to heat activate such nontacky surface over the relatively long period of ten seconds is contrary to the goal of achieving manufacturing efficiency, and thus is not economically practical.
Additionally, in practice it is known that the patented two-layer adhesive coating is not effective at forming a completely nonblocking PSA construction, thereby permitting adhesional interference to occur between contiguous PSA construction surfaces. Such blocking is believed to be caused by the failure of nontacky surface to form a completely continuous film to cover the underlying adhesive layer.
U.S. Pat. No. 3,843,480 discloses a process for preparing a surface-detack layer on a PSA that is carried releasably upon a supporting release liner. The process includes the steps of applying a PSA layer onto a release liner and dusting a surface portion of the PSA layer with a mineral powder to detackify the PSA layer. The resulting detackified PSA layer is said to permit the prelaminate construction to be wound upon itself or sheeted and stacked without adhesional interference. However, in practice it is known that such patented prelaminate constructions are not completely effective at preventing blocking, as adhesional interference between contiguous construction layers is known to occur. A reason for such blocking is believed to be the failure of the mineral powder to form a continuous PSA covering film.
The surface detack layer of such patented construction is subsequently attached to another substrate surface, such as printing paper and the like, by a single process step of simultaneously heating the surface of both the detack layer and the printing paper, while applying pressure to the printing paper and heated detack layer to form a completed laminate construction.
Simultaneous heat activation of the detack layer and pressure lamination, however, is problematic because it limits the types of substrate materials that can be used. For example, thermally-sensitive substrates such as thermal print paper, films of polymers having a low glass transition temperature, and oriented polymer films cannot be used with this process because the step of heating such substrates is known to adversely impact the desired performance of these materials.
The need to simultaneously heat activate and laminate the PSA construction is also not desired because of the related problems that are known to occur at the nip, such as wrinkling and buckling of the laminated construction that is caused by the different coefficients of expansion between the prelaminate PSA construction and the laminated substrate. Additionally, simultaneous heat activation and lamination is also known to cause shrinkage in paper face stocks due to the loss of water that occurs during such heat exposure, which is known to cause curling and the like. Simultaneous heat activation and lamination can also cause the outgassing of steam or other vapors in the nip, which is known to result in bubble formation at the nip and produce a laminate construction having areas of poor anchorage.
U.S. Pat. No. 3,343,978 discloses an adhesive structure comprising a flexible substrate, a PSA in contact with the substrate, and a nontacky layer adhering to the surface of the PSA. The nontacky layer can be formed from a material that is subsequently heat activated to form a second tacky layer, which is simultaneously heat laminated to a desired first article. The flexible substrate is removed to expose the PSA, which is placed into contact with a desired second article.
Again, the need to heat laminate the first article to an activated tacky layer, when using a heat activatable nontacky layer, limits the types of first articles capable of being used with the adhesive structure to those that are not affected by exposure to high temperatures, and introduces the numerous problems described above that are encountered during heated lamination.
U.S. Pat. No. 3,027,271 discloses a PSA composite comprising a face stock, a PSA tacky layer deposited onto the surface of the face stock, and a dry powder layer deposited onto the surface of the PSA tacky layer. The dry powder is intended to detackify the underlying PSA tacky layer and, in theory, allow the face stock material to be stored or stacked without sticking to itself The dry powder layer is formed from dry particles that are removable upon application of heat by vaporization or decomposition into gaseous products, thereby exposing the underlying tacky layer for application of the composite at the point of use.
As discussed above with reference to the construction described in U.S. Pat. No. 3,843,480, the use of a dry powder in this patented composite also fails to provide a completely nonblocking PSA composite, thereby permitting adhesional interference to occur between contiguous surfaces of the PSA composite. The reason for this is believed to be the failure of the dry powder layer to form a continuous PSA covering film.
Having to heat the composite to remove or vaporize the dry powder layer and expose the PSA tacky layer, again limits the type of face stocks that can be used to form the composite to those not affected by exposure to high temperatures. Additionally, the patented composite that is disclosed is one that includes a face stock and, therefore, does not address the desire to provide a face stock-free prelaminate PSA construction.
It is, therefore, desired that prelaminate PSA constructions be designed and manufactured to have nonblocking properties enabling such prelaminate PSA constructions to be collected in roll form or the like and stored without adhering to contiguous layers for subsequent lamination to a substrate. It is desired that prelaminate PSA constructions be capable of being activated in a relatively short amount of time prior to lamination with a substrate to maximize manufacturing efficiency. It is also desired that prelaminate PSA constructions be capable of facilitating lamination at temperature conditions that do not limit the types of laminating substrate that can be used, and that avoid problems known to occur during heated lamination. It is further desired that the prelaminate PSA construction be capable of facilitating lamination without the emission or use of potentially dangerous or harmful gases or chemicals.
Additionally, it is desired to provide a process for adhesively activating and later laminating a prelaminate construction to a substrate. Such process should avoid the problems of heated lamination, and should afford manufacturing flexibility. For example, such process should permit the insertion or application of an additional layer or structure after adhesive activation and before lamination to the substrate; and should allow the lamination of a variety of types of flexible substrates to the adhesively activated prelaminate construction.
There is provided in the practice of this invention, prelaminate PSA constructions manufactured without second substrates, e.g., face stocks, that introduce manufacturing flexibility into the process of making laminated PSA constructions. Prelaminate PSA constructions of this invention are nonblocking, thereby eliminating the possibility of adhesive interference occurring between the prelaminate PSA construction and a contiguous surface. Prelaminate PSA constructions of this invention are activatable in less than about five seconds to permit subsequent lamination to a second substrate at a temperature less than about 100xc2x0 C., i.e., a temperature significantly below a heat activation temperature.
Prelaminate PSA constructions of this invention comprise, a first substrate having a layer releasable material disposed thereon, a PSA layer disposed on the layer of releasable material, and a detackified layer (DL) disposed on a surface of the PSA layer. The DL can be formed from, in first and second construction embodiments, a detackifying material that is activatable to form a tacky layer on top of the PSA layer; and in a third construction embodiment, from a detackifying material that is activatable to migrate into the PSA layer and reveal the PSA layer tacky surface. Preferred first and third embodiment detackifying materials are heat activatable, while preferred second embodiment detackifying materials are chemically activatable. In each instance the tacky surface is provided to accommodate subsequent lamination to a second substrate for forming a laminated PSA construction.
Prelaminate PSA constructions of this invention are completely nonblocking to a minimum 24 hour blocking temperature of at least 50xc2x0 C. at a pressure of about 40 kilopascals (kPa). The nonblocking characteristics of the prelaminate PSA construction permits lamination to occur either: (1) after the step of manufacturing the prelaminate PSA construction during the same process operation; (2) after the step of manufacturing the prelaminate PSA construction during a separate process operation at the same geographic location; or (3) after the step of manufacturing the prelaminate PSA construction during a separate process operation at a different geographic location.
Laminated PSA constructions of this invention, prepared from first and second embodiment prelaminate PSA constructions, comprise a first flexible substrate having a layer of releasable material disposed thereon, a layer of PSA disposed on the layer of releasable material, a DL disposed on a surface of the PSA layer, and a second substrate laminated to a surface of the DL. Laminated PSA constructions formed from first embodiment prelaminate PSA construction have improved properties of structural rigidity and shear when compared to conventional laminated PSA constructions that do not include the DL. For this reason, the DL in such embodiment is a reinforcing material.
Furthermore, the DL of the first and second embodiment prelaminate PSA constructions acts as a barrier to prevent the migration of low-molecular weight species from the pressure sensitive adhesive to the second substrate, which can stain the second substrate.
Laminated PSA constructions of this invention, prepared from a third embodiment prelaminate PSA construction, comprises a first flexible substrate having a layer of low-release material disposed thereon, a layer of PSA disposed on the layer of low-release material that includes detackifying material constituents disposed therein, and a second substrate laminated to a surface of the PSA layer.
Prelarninate PSA constructions of this invention: (1) introduce flexibility into the process of manufacturing PSA construction by allowing the prelaminate PSA constructions to be stored, handled or transported before lamination, thereby eliminating the need to laminate immediately after PSA formation; (2) permit lamination at low or ambient process temperature conditions, thereby maximizing the type of substrates that can be used with the construction and eliminating problems that are otherwise known to occur during heated lamination; and (3) enhance the physical properties of the laminated PSA construction.